1. Field of the Invention
This invention relates to a composite unit including metal and resin and a process of producing the same, and more particularly to improvements in sealing properties between the contact surfaces of a metal member and a resin structure, said sealing properties being concerned with an effective technique utilized, for example, in a composite unit including a metal bracket and a resin brush holder (hereinafter referred to as "a bracket unit") used in a revolving electric machine such as a starter motor, wherein the brush holder is resin-molded integrally on a portion of the bracket.
2. Related Art Statement
As a bracket unit used in a starter motor, there has been proposed one wherein a resin brush holder is formed integrally with a bracket of a thin plate shape (refer to Japanese Utility Model Laid-Open 61-58834 for example).
Now, the inventors of the present invention have clarified that, in the brush holder of the type described, when an Fe group material is used in the bracket and a polyamide resin is used in the brush holder, respectively, if environmental tests such as thermal shock tests are conducted, then, because of difference in the coefficients of thermal expansion of the bracket and the brush holder, a relative displacement occurs between contact surfaces thereof, with the result that air-tightness and liquid-tightness are lowered in a housing of the starter motor to which this bracket unit is attached.